Systems and Methods of Controlling In Situ Resistive Heating Elements

ABSTRACT

Systems and methods for controlling in situ resistive heating elements may be utilized to enhance hydrocarbon production within a subterranean formation. An in situ resistive heating element may be controlled by heating a controlled region associated with the in situ resistive heating element, injecting a control gas into the controlled region, and adjusting the electrical conductivity of the controlled region with the control gas. The controlled region may be located such that the heating and injecting may change the shape of the in situ resistive heating element and/or guide the in situ resistive heating element towards subterranean regions of potentially higher productivity and/or of higher organic matter.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. Provisional Patent Application 61/901,252 filed Nov. 7, 2013 entitled SYSTEMS AND METHODS OF CONTROLLING IN SITU RESISTIVE HEATING ELEMENTS, the entirety of which is incorporated by reference herein.

FIELD

The present disclosure is directed generally to systems and methods of controlling in situ resistive heating elements, and more specifically to systems and methods for adjusting the electrical conductivity of regions of a subterranean formation containing an in situ resistive heating element.

BACKGROUND

Certain subterranean formations may include organic matter, such as shale oil, bitumen, and/or kerogen, which have material and chemical properties that may complicate production of hydrocarbons from the subterranean formations. For example, the organic matter may not flow at a rate sufficient for production. Moreover, the organic matter may not include sufficient quantities of desired chemical compositions (typically smaller hydrocarbons). Hence, recovery of useful hydrocarbons from such subterranean formations may be uneconomical or impractical.

Generally, organic matter is subject to decompose upon exposure to heat over a period of time, via a process called pyrolysis. Upon pyrolysis, organic matter, such as kerogen, may decompose chemically to produce hydrocarbon oil, hydrocarbon gas, and carbonaceous residue (the residue may be referred to generally as coke). Coke formed by pyrolysis typically has a richer carbon content than the source organic matter from which it was formed. Small amounts of water also may be generated via the pyrolysis reaction. The oil, gas, and water fluids may become mobile within the rock or other subterranean matrix, while the residue coke remains essentially immobile.

One method of heating and causing pyrolysis includes using electrically resistive heaters placed within the subterranean formation. However, conventional electrically resistive heaters, such as wellbore heaters, have a limited heating range. Though heating may occur by radiation and/or conduction to heat materials far from the well, to do so, a conventional heater typically will heat the region near the well to very high temperatures for very long times. In essence, conventional methods for heating regions of a subterranean formation far from a well may involve overheating the nearby material in an attempt to heat the distant material. Such uneven application of heat may result in suboptimal production from the subterranean formation. Additionally, using wellbore heaters in a dense array to mitigate the limited heating distance may be cumbersome and expensive.

Other types of electrically resistive heaters may heat a larger subterranean region and/or may have a larger heating range. As an example, granular resistive heaters may include an extended heating element of electrically conductive material (typically coke, graphite, and/or metal particles) inserted into a natural and/or manmade fracture in a subterranean formation. In situ resistive heaters may include an extended heating element formed from pyrolyzed organic material in a subterranean formation. Both types of extended resistive heating elements may heat an extended region of the subterranean formation near the heating element. However, the electrical power required to effectively heat an extended heating element grows approximately proportional to the length of the extended heating element. Hence, the power requirements for an extended heating element may be prohibitively expensive and impractical.

Further, an in situ resistive heating element may grow as it heats neighboring subterranean regions. As an in situ resistive heating element grows, the electrical power required to continue heating the in situ resistive heating element likewise grows, potentially leading to an impractically large power requirement.

Thus, there exists a need for more economical and efficient heating of subterranean formations.

SUMMARY

The present disclosure provides systems and methods for controlling in situ resistive heating elements to enhance hydrocarbon production within a subterranean formation.

A method of controlling an in situ resistive heating element within a subterranean formation. The method may comprise heating the controlled region with the in situ resistive heating element, injecting a control gas into the controlled region, and adjusting the electrical conductivity of the controlled region with the control gas.

A system to control an in situ resistive heating element within a subterranean formation. The system may adjust the electrical conductivity of a controlled region within the subterranean formation. The system may comprise an in situ resistive heater to heat a controlled region, a gas delivery system to inject a control gas into the controlled region and to adjust an electrical conductivity of the controlled region with the control gas, and a sensor to monitor a parameter relating to at least one of the subterranean formation, the in situ resistive heater, the gas delivery system and/or the controlled region. The in situ resistive heater may include an in situ resistive heating element within the subterranean formation and electrically connected to two or more spaced-apart electrodes. The in situ resistive heater further may include an electrical power source electrically connected through a pair of spaced-apart electrodes to the in situ resistive heating element. The gas delivery system may include a gas injection well that is fluidically connected to the controlled region and a gas source configured to supply the control gas to the gas injection well. The control gas may be selected to affect, or otherwise adjust, the electrical conductivity of the controlled region. The parameter includes at least one of an electrical conductivity, an electrical property, an electrical power, an electrical current, a temperature, a pressure, a gas composition, a chemical environment, and a chemical redox state.

The foregoing has broadly outlined the features of the present disclosure so that the detailed description that follows may be better understood. Additional features also will be described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the disclosure will become apparent from the following description, appending claims and the accompanying drawings, which are briefly described below.

FIG. 1 is a schematic cross-sectional view of a system to control an in situ resistive heating element within a subterranean formation.

FIG. 2 is a flow chart of methods to control an in situ resistive heating element.

FIG. 3 is a schematic representation of results of controlling an in situ resistive heating element showing a decrease in electrical conductivity of a controlled region.

FIG. 4 is a schematic representation of results of controlling an in situ resistive heating element by splitting the in situ resistive heating element.

FIG. 5 is a schematic representation of results of controlling an in situ resistive heating element showing an increase in electrical conductivity of a controlled region.

FIG. 6 is a schematic representation of results of controlling an in situ resistive heating element showing a controlled region initially outside of the in situ resistive heating element.

FIG. 7 is a schematic representation of results of controlling an in situ resistive heating element showing a controlled region restricting expansion of an in situ resistive heating element.

It should be noted that the figures are merely examples and no limitations on the scope of the present disclosure are intended thereby. Further, the figures are generally not drawn to scale, but are drafted for purposes of convenience and clarity in illustrating various aspects of the disclosure.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the features illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended. Any alterations and further modifications, and any further applications of the principles of the disclosure as described herein are contemplated as would normally occur to one skilled in the art to which the disclosure relates. It will be apparent to those skilled in the relevant art that some features that are not relevant to the present disclosure may not be shown in the drawings for the sake of clarity.

Thermal generation and stimulation techniques may be used to produce subterranean hydrocarbons within, for example, subterranean regions within a subterranean formation which contain and/or include organic matter, and which may include large hydrocarbon molecules (e.g., heavy oil, bitumen, and/or kerogen). Hydrocarbons may be produced by heating. In some instances, it may be desirable to perform in situ upgrading of the hydrocarbons, i.e., conversion of the organic matter to more mobile forms (e.g., gas or liquid) and/or to more useful forms (e.g., smaller, energy-dense molecules). In situ upgrading may include performing at least one of a shale oil retort process, a shale oil heat treating process, a hydrogenation reaction, a thermal dissolution process, and an in situ shale oil conversion process. An shale oil retort process, which also may be referred to as destructive distillation, involves heating oil shale in the absence of oxygen until kerogen within the oil shale decomposes into liquid and/or gaseous hydrocarbons. In situ upgrading via a hydrogenation reaction includes reacting organic matter with molecular hydrogen to reduce, or saturate, hydrocarbons within the organic matter. In situ upgrading via a thermal dissolution process includes using hydrogen donors and/or solvents to dissolve organic matter and to crack kerogen and more complex hydrocarbons in the organic matter into shorter hydrocarbons. Ultimately, the in situ upgrading may result in hydrocarbons that may be extracted from the subterranean formation.

FIGS. 1-7 provide examples of systems, configurations, and/or methods to control an in situ resistive heating element 40 within a subterranean formation 28 for efficient in situ upgrading. Elements that serve a similar, or at least substantially similar, purpose are labeled with like numbers in each of FIGS. 1-7. Each of these elements may not be discussed in detail with reference to each of FIGS. 1-7. Similarly, all elements may not be labeled in each of FIGS. 1-7, but reference numerals associated therewith may be used for consistency. Elements that are discussed with reference to one or more of FIGS. 1-7 may be included in and/or used with any of FIGS. 1-7 without departing from the scope of the present disclosure. In general, elements that are likely to be included are illustrated in solid lines, while elements that are optional are illustrated in dashed lines. However, elements that are shown in solid lines may not be essential. Thus, an element shown in solid lines may be omitted without departing from the scope of the present disclosure.

FIG. 1 schematically depicts examples of systems 30 for controlling an in situ resistive heating element 40 within a subterranean formation 28 using one or more controlled regions 70. The subterranean formation 28 includes organic matter. Systems 30 may comprise an in situ resistive heater 38 to heat a controlled region 70 and a gas delivery system 36 to inject the control gas 68 into the controlled region 70 and to adjust an electrical conductivity of the controlled region 70 with the control gas 68. Systems 30 may comprise a sensor 32 to monitor a parameter relating to at least one of the subterranean formation 28, the in situ resistive heater 38, the gas delivery system 36, and the controlled region 70.

An in situ resistive heater 38 may include an in situ resistive heating element 40. An in situ resistive heating element 40 is an electrically conductive zone within a subterranean formation 28. Though bulk rock within a subterranean formation typically has low electrical conductivity, upon heating, organic matter within the bulk rock may pyrolyze and create a zone of higher electrical conductivity within the heated region. When an electrical current is transmitted through the in situ resistive heating element 40, ohmic losses may cause significant resistive heating within the heating element 40. This heating may heat the heating element 40 and neighboring (i.e., adjacent, nearby, abutting, and/or contiguous) subterranean regions. If the heated neighboring regions contain organic matter, the regions may pyrolyze and become more electrically conductive. Under voltage-limited conditions (e.g., approximately constant voltage conditions), an increase in conductivity (decrease in resistivity) causes increased resistive heating. Hence, as electrical power is applied to the in situ resistive heating element 40, the heating of neighboring regions may create an expanding, aggregate electrically conductive zone and an expanding in situ resistive heating element 40. Transmitted electrical current may spread through the expanding in situ resistive heating element 40, causing further heating of more neighboring regions and further expansion. This expansion may continue while sufficient electrical power is available to cause sufficient heating within the expanding in situ resistive heating element 40. An in situ resistive heating element 40 that can expand, such as due to the heat produced by the resistive heating element, also may be referred to as a self-amplifying heating element.

The in situ resistive heating element 40 may define a volume within the subterranean formation 28 with an exterior volume 81, an enclosed volume 83, and/or an interior volume 82. The exterior volume 81 is the total volume of the environment occupied by the heating element. The enclosed volume 83 is an internal void; an inactive volume separated from the exterior of the heating element. The interior volume 82 is the active volume of the heating element, not including any enclosed volume. By way of context, if an object is solid (i.e., filled, without voids), the exterior volume is the same as the interior volume. If an object is hollow or encloses voids, the interior volume is the exterior volume minus the volume of the voids. For example, the exterior volume of a hollow glass sphere is the volume of the exterior of the sphere. The enclosed volume of the hollow sphere is the volume of the hollow, i.e., the volume enclosed by the interior surface of the glass. The interior volume of such a sphere is the exterior volume minus the volume of the hollow. Alternatively stated, the interior volume of such a sphere is the volume of the glass. Thus, in the context of an in situ, resistive heating element, the in situ resistive heating element may define a shell structure with a shell volume (an interior volume) and a core volume substantially enclosed by the shell volume. The core volume may be an enclosed volume if completely enclosed by the shell volume.

The interior volume 82 of an in situ resistive heating element 40 is a contiguous volume of the electrically conductive zone that has an electrical conductivity high enough for current to flow to generate sufficient resistive heating when electrical power is applied to the heating element. When electrically powered, the interior volume 82 of an in situ resistive heating element 40 is the volume that actively heats due to resistive heating. Hence, the interior volume 82 of an in situ resistive heating element 40 may sometimes be referred to as the active volume of the in situ resistive heating element.

A subterranean formation 28 may be any suitable structure that includes and/or contains organic matter. Examples of organic matter included, but are not limited to oil shale, shale gas, coal, tar sands, organic-rich rock, kerogen, and/or bitumen. The subterranean formation 28 may be a geological formation, a geological member, a geological bed, a rock stratum, a lithostratigraphic unit, a chemostratigraphic unit, and/or a biostratigraphic unit, or groups thereof. The subterranean formation 28 may have a thickness less than 2000 m, less than 1500 m, less than 1000 m, less than 500 m, less than 250 m, less than 100 m, less than 80 m, less than 60 m, less than 40 m, less than 30 m, less than 20 m, less than 10 m, and/or within a range that includes or is bounded by any of the preceding examples of thicknesses. The subterranean formation 28 may have a thickness that is greater than 5 m, greater than 10 m, greater than 20 m, greater than 30 m, greater than 40 m, greater than 60 m, greater than 80 m, greater than 100 m, greater than 250 m, greater than 500 m, greater than 1000 m, greater than 1500 m, and/or within a range that includes or is bounded by any of the preceding examples of thicknesses.

Pyrolysis, a form of thermochemical decomposition, may transform organic matter within a subterranean formation 28 into at least one of liquid hydrocarbons, gaseous hydrocarbons, shale oil, bitumen, pyrobitumen, bituminous coal, and coke. For example, pyrolysis of kerogen may result in hydrocarbon gas, shale oil, and/or coke. Generally, pyrolysis occurs at elevated temperatures. For example, pyrolysis may occur at temperatures of at least 250° C., at least 350° C., at least 450° C., at least 550° C., at least 700° C., at least 800° C., and/or at least 900° C. As additional examples, in some situations it may be desirable not to overheat the region to be pyrolyzed. Examples of pyrolyzation temperatures include temperatures that are less than 1000° C., less than 900° C., less than 800° C., less than 700° C., less than 550° C., less than 450° C., less than 350° C., and/or less than 270° C. As additional examples, pyrolysis may occur and/or be performed at any of the preceding examples of minimum and maximum temperatures, and/or at temperature ranges that include and/or are by any of the preceding examples of minimum and maximum temperatures.

Bulk rock in a subterranean formation 28 generally has a low electrical conductivity (equivalently, a high electrical resistivity), typically on the order of 10⁻⁷-10⁻⁴ S/m (a resistivity of about 10⁴-10⁷ Ωm). For example, the average electrical conductivity within a subterranean formation, or a region within the subterranean formation, may be less than 10⁻³ S/m, less than 10⁻⁴ S/m, less than 10⁻⁵ S/m, less than 10⁻⁶ S/m, and/or within a range that includes or is bounded by any of the preceding examples of average electrical conductivities. Most types of organic matter found in subterranean formations have similarly low conductivities. However, the residual coke resulting from pyrolysis is relatively enriched in carbon and has a relatively higher electrical conductivity. For example, Green River oil shale (a rock including kerogen) may have an average electrical conductivity in ambient conditions of about 10⁻⁷-10⁻⁶ S/m. As the Green River oil shale is heated to between about 300° C. and about 600° C., the average electrical conductivity may rise to greater than 10⁻⁵ S/m, greater than 1 S/m, greater than 100 S/m, greater than 1,000 S/m, even greater than 10,000 S/m, or within a range that includes or is bounded by any of the preceding examples of electrical conductivity. This increased electrical conductivity may remain even after the rock returns to lower temperatures.

Continued heating (increasing temperature and/or longer duration) may not result in further increases of the electrical conductivity of a subterranean region. Other components of the subterranean formation 28, e.g., carbonate minerals such as dolomite and calcite, may decompose at a temperature similar to useful pyrolysis temperatures. For example, dolomite may decompose at about 550° C., while calcite may decompose at about 700° C. Decomposition of carbonate minerals generally results in carbon dioxide, which may reduce the electrical conductivity of subterranean regions neighboring the decomposition. For example, decomposition may result in an average electrical conductivity in the subterranean region(s) of less than 0.1 S/m, less than 0.01 S/m, less than 10⁻³ S/m, less than 10⁻⁴ S/m, less than 10⁻⁵ S/m, and/or within a range that includes or is bounded by any of the preceding examples of average electrical conductivity.

If a pyrolyzed subterranean region has sufficient electrical conductivity, generally greater than about 10⁻⁵ S/m, the region may be described as an electrically conductive zone. An electrically conductive zone may include bitumen, pyrobitumen, bituminous coal, and/or coke produced by pyrolysis. An electrically conductive zone is a region within a subterranean formation 28 that has an electrical conductivity greater than, typically significantly greater than, the unaffected bulk rock of the subterranean formation 28. For example, the average electrical conductivity of an electrically conductive zone may be at least 10⁻⁵ S/m, at least 10⁻⁴ S/m, at least 10⁻³ S/m, at least 0.01 S/m, at least 0.1 S/m, at least 1 S/m, at least 10 S/m, at least 100 S/m, at least 300 S/m, at least 1,000 S/m, at least 3,000 S/m, at least 10,000 S/m, and/or within a range that includes or is bounded by any of the preceding examples of average electrical conductivity.

The residual coke after pyrolysis may form an electrically conductive zone that may be used to conduct electricity and act as an in situ resistive heating element 40 for continued upgrading of the hydrocarbons. An in situ resistive heating element 40 may include an electrically conductive zone that has an electrical conductivity sufficient to cause ohmic losses, and thus resistive heating. For example, the average electrical conductivity of an in situ resistive heating element 40 may be at least 10⁻⁵ S/m, at least 10⁻⁴ S/m, at least 10⁻³ S/m, at least 0.01 S/m, at least 0.1 S/m, at least 1 S/m, at least 10 S/m, at least 100 S/m, at least 300 S/m, at least 1,000 S/m, at least 3,000 S/m, at least 10,000 S/m, and/or within a range that includes or is bounded by any of the preceding examples of average electrical conductivity.

The in situ resistive heater 38 may include and/or be in electrical communication with an electrical system to electrically power the in situ resistive heating element 40. The electrical system may include an electrical power source 31 to supply electrical current through the in situ resistive heating element 40. The electrical system may be electrically connected in a circuit to the in situ resistive heating element 40 via two or more spaced-apart electrodes 50. Typically, the two or more spaced-apart electrodes 50 are operated in sets of two electrodes. Electrical power may be transmitted between more than two electrodes 50. For example, two electrodes 50 may be held at the same electrical potential while a third electrode 50 is held at a different potential. As another example, two or more electrodes may transmit AC power with each electrode transmitting a different phase of the power signal.

Electrodes 50 may be electrically conductive elements, typically including metal and/or carbon. Electrodes 50 may be in electrical contact with a portion of the subterranean formation 28. Electrical contact includes contact sufficient to transmit electrical power, including AC and DC power. Electrical contact may be established between two elements by direct contact between the elements. Two elements may be in electrical contact when indirectly linked by intervening elements, provided that the intervening elements are at least as conductive as the less conductive of the two connected elements, i.e., the intervening elements do not dominate current flow between the elements in contact. The conductance of an element is proportional to its conductivity and its cross sectional area, and inversely proportional to its current path length. Hence, small elements with low conductivities may have high conductance.

Whether a subterranean region is poorly electrically conductive (e.g., having an electrical conductivity below 10⁻⁴ S/m) or not poorly electrically conductive (e.g., having an electrical conductivity above 10⁻⁴ S/m and alternatively referred to as highly electrically conductive), an electrode 50 may be in electrical contact with the subterranean region 28 by direct contact between the electrode 50 and the region and/or by indirect contact via suitable conductive intervening elements. For example, remnants from drilling fluid (mud), though typically not highly electrically conductive (typical conductivities range from 10⁻⁵ S/m to 1 S/m), may be sufficiently electrically conductive to provide suitable electrical contact between an electrode 50 and a subterranean region.

Where an electrode 50 is situated within a wellbore, the electrode may be engaged directly against the wellbore, or an electrically conductive portion of the casing of the wellbore. The situating of the electrode 50 within the wellbore may cause electrical contact between the electrode and the subterranean region surrounding the wellbore. The electrode 50 may be in electrical contact with a subterranean region through subterranean spaces (e.g., natural and/or manmade fractures; voids created by hydrocarbon production) filled with electrically conductive materials (e.g., graphite, coke, and/or metal particles).

Electrodes 50 may be contained at least partially within an electrode well 60 in the subterranean formation 28. Electrodes 50 may be placed at least partially within an electrode well 60. Electrode wells 60 may include one or more electrodes 50. In the case of multiple electrodes 50 being contained within one electrode well 60, the electrodes 50 may be spaced apart and insulated from each other. An electrode 50 may extend outside of an electrode well 60 and into the subterranean formation 28, for example, through a natural and/or manmade fracture.

An electrode well 60 may include an end portion that may contain at least one electrode 50. End portions of electrode wells 60 may have a specific orientation relative to the subterranean formation 28, regions of the subterranean formation 28, and/or other electrode wells 60. As examples, the end portion of one of the electrode wells 60 may be co-linear with, and spaced apart from, the end portion of another of the electrode wells 60. The end portion of one of the electrode wells 60 may be at least one of substantially parallel, parallel, substantially co-planar, and co-planar to the end portion of another of the electrode wells 60. The end portion of one of the electrode wells 60 may converge toward or diverge away from the end portion of another of the electrode wells 60. Where at least one of the subterranean formation 28, a region of the subterranean formation 28, and an in situ resistive heating element 40 is elongate with an elongate direction, the end portion of one of the electrode wells 60 may be at least one of substantially parallel, parallel, oblique, substantially perpendicular, and perpendicular to the elongate direction. Electrode wells 60 may include a portion, optionally including the end portion, that may be at least one of horizontal, substantially horizontal, inclined, vertical, and substantially vertical. Electrode wells 60 also may include a differently oriented portion, which may be at least one of horizontal, substantially horizontal, inclined, vertical, and substantially vertical.

Systems 30 may comprise one or more controlled regions 70 within the subterranean formation 28. Each controlled region 70 is a region of the subterranean formation 28 that may be heated and pyrolyzed by the in situ resistive heater 38. Each controlled region 70 is a region that may be affected by the gas delivery system 36, such as by adjusting the electrical conductivity of the controlled region 70 responsive to the delivery of one or more control gases, such as by injection of one or more control gases to the controlled region 70. Upon heating, changes in electrical conductivity may be affected by the control gas 68, which may be delivered by the gas delivery system 36. The electrical conductivity of each controlled region 70 may be controlled by controlling the chemical environment during pyrolysis (e.g., controlling the redox state of pyrolysis products). Carbonaceous coke produced by pyrolysis in the absence of oxidizing agents has a relatively high electrical conductivity. However, in the presence of oxidizing agents, the coke may be oxidized to a lower electrical conductivity composition.

A controlled region 70 may be inside, outside, and/or near the in situ resistive heating element 40. Inside the in situ resistive heating element 40 refers to inside the interior volume of the in situ resistive heating element 40. Outside the in situ resistive heating element 40 refers to outside the exterior volume and/or inside any enclosed volume of the in situ resistive heating element 40. Near the in situ resistive heating element 40 includes adjacent to, proximate to, adjoining, abutting, intersecting, and/or at least partially overlapping the in situ resistive heating element 40. A controlled region 70 may be at least partially inside and at least partially outside the in situ resistive heating element 40. When the in situ resistive heating element 40 defines a shell structure with a core volume, each controlled region 70 may be at least partially within the shell volume and/or the core volume. A controlled region 70 may be between an in situ resistive heating element 40 and a restricted region 72, which refers to a region in which the self-amplifying heating element cannot and/or is not intended to expand. For example, a restricted region 72 may be or include an aquifer, another in situ resistive heating element 40, and/or a ‘spent’ region of the subterranean formation (e.g., a pyrolyzed region and/or a region where upgraded hydrocarbons have been extracted). When a controlled region is between an in situ resistive heating element and a restricted region, the controlled region may be said to buffer and/or protect the restricted region by limiting expansion of the in situ resistive heating element into the restricted region.

Systems 30 may comprise a gas delivery system 36 that is configured to inject one or more control gases 68 into one or more controlled regions 70 and to adjust the electrical conductivity of the one or more controlled regions 70 with the one or more control gases 68. The gas delivery system may include a gas injection well 62 fluidically connected to one or more controlled regions 70. More than one gas injection well may be fluidically connected to the same controlled region 70. The fluidic connection between the gas delivery system 36 and the one or more controlled regions 70 allows a pathway for control gases 68 to enter the one or more controlled regions. The gas delivery system 36 may include one or more gas sources 35 configured to supply one or more control gases to the gas injection well(s). Each gas source 35 may include the atmosphere, a gas tank, and/or the subterranean formation (e.g., gases produced within one portion of the subterranean formation may be injected into one or more controlled regions).

The gas delivery system 36 may be used to affect, or otherwise adjust, the electrical conductivity of one or more controlled regions 70 during heating of one or more controlled regions 70. For example, the gas delivery system 36 may affect the chemical environment of one or more controlled regions 70 by the injection of the one or more control gases 68. Furthermore, the electrical conductivity of the one or more controlled regions 70 may be adjusted by the chemical environment on account of the injection of the one or more control gases 68. For example, oxidizing agents within one or more controlled regions 70 typically decrease the electrical conductivity, or mitigate the electrical conductivity increase, associated with pyrolyzation. Oxidizing agents may be introduced to one or more controlled regions 70 (e.g., through the gas delivery system 36) and/or may be produced within the subterranean formation 28. Oxidizing agents may be removed from one or more controlled regions 70 and/or consumed within one or more controlled regions, which may result in increasing electrical conductivity, or mitigating the decrease in electrical conductivity, associated with pyrolyzation. Oxidizing agents may be produced and/or consumed within one or more controlled regions 70 by the introduction of a reactant to one or more controlled regions 70 through the gas delivery system 36. Oxidizing agents may be produced and/or or consumed within one or more controlled regions 70 by chemical reactions activated and/or accelerated by heating one or more controlled regions. For example, carbonate minerals in a subterranean formation may decompose upon sufficient heating to produce carbon dioxide, an oxidizing gas.

Precise control of the chemical environment, and/or the redox state, of one or more controlled regions 70 may be achieved by injecting a control gas 68 of known chemical properties into one or more controlled regions 70. The gas delivery system 36 may be configured to inject oxidizing gas into one or more controlled regions such that heating one or more controlled regions would not significantly increase the electrical conductivity of one or more controlled regions. The gas delivery system 36 may inject non-oxidizing gas (e.g., inert gas and/or reducing gas) into one or more controlled regions such that, upon heating, the electrical conductivity of one or more controlled regions would not be significantly altered by oxidizing agents. Introduced non-oxidizing gas may react with any oxidizing agents produced in and/or transported to one or more controlled regions. Introduced non-oxidizing gas may reduce the partial pressure (concentration) of oxidizing agents within the one or more controlled regions.

The gas delivery system 36 may deliver a plurality of control gases 68 to the one or more controlled regions 70. The plurality of control gases may include oxidizing gases and non-oxidizing gases. The gas delivery system may deliver the control gases at least partially sequentially.

Gas injection wells 62 may include a fluidic connection from above ground to the subterranean formation 28. A gas injection well 62 may include portions that are natural and/or manmade. A gas injection well 62 may include an injection site 63, which may be near one or more controlled regions 70. The injection site 63 may be configured to allow fluid to flow from the injection site into one or more controlled regions. For example, the injection site 63 may be porous and/or perforated. The injection site 63 may be essentially an injection point or may be a spatially extended portion of the gas injection well 62. The gas injection well 62, except for the injection site 63, may be substantially fluid tight, generally retaining fluid within the gas injection well.

A gas injection well 62 may include an end portion that may include one or more injection sites 63. Each end portion of a gas injection well may have a specific orientation relative to the subterranean formation 28, the in situ resistive heating element 40, and/or other wells (such as electrode wells 60, gas injection wells 62, and production wells 64). For example, where at least one of the subterranean formation 28 and an in situ resistive heating element 40 is elongate with an elongate direction, the end portion of one of the gas injection wells 62 may be at least one of substantially parallel, parallel, oblique, substantially perpendicular, and perpendicular to the elongate direction. Gas injection wells 62 may include a portion, optionally including the end portion, that may be at least one of horizontal, substantially horizontal, inclined, vertical, and substantially vertical. Gas injection wells 62 also may include a differently oriented portion, which may be at least one of horizontal, substantially horizontal, inclined, vertical, and substantially vertical.

When present, an electrode well 60 may also be a gas injection well 62. A combination electrode and gas injection well may contain an electrode 50 in electrical contact with an in situ resistive heating element 40. A combination electrode and gas injection well may deliver gas to the controlled region 70.

The control gas 68 may be an oxidizing gas, which may be used to decrease and/or to maintain the electrical conductivity of one or more controlled regions by oxidizing while pyrolyzing the controlled region. The control gas 68 may be a reducing gas, which may be used to increase and/or to maintain the electrical conductivity of one or more controlled regions by reducing (and/or inhibiting oxidization) while pyrolyzing one or more controlled regions. The control gas 68 may be a sweep gas (e.g., a substantially inert gas, a substantially non-oxidizing gas, and/or a gas that is substantially non-reactive with at least one of the controlled region and coke), which may be used to increase and/or maintain the electrical conductivity of one or more controlled regions by limiting the partial pressure (concentration) of oxidizing gases while pyrolyzing one or more controlled regions. The control gas 68 may be a gas mixture, a gas composition, an aerosol, or a gaseous suspension. The control gas 68 may be substantially composed of at least one of carbon dioxide (CO₂), oxygen (O₂), air, steam, hydrogen sulfide (H₂S), methane, hydrocarbon gas, nitrogen (N₂), argon, carbon monoxide (CO), and hydrogen (H₂).

Systems 30 may comprise a sensor 32. The sensor 32 may monitor a parameter relating to at least one of the subterranean formation 28, the in situ resistive heater 38, the gas delivery system 36, and the one or more controlled regions 70. As examples, the monitored parameter may include geophysical data relating to the shape, extent, volume, composition, density, porosity, permeability, electrical conductivity, electrical property, temperature, and/or pressure of at least one of the subterranean formation 28, the in situ resistive heating element 40, and the one or more controlled regions 70. The monitored parameter may relate to the production of mobile components within the subterranean formation 28 (e.g., hydrocarbon production). The monitored parameter may relate to the electrical power applied to the in situ resistive heating element. For example, the monitored parameter may include the at least one of the duration of applied electrical power, the magnitude of electrical power applied, and the magnitude of electrical current transmitted. The magnitude of electrical power applied and/or electrical current transmitted may include the average value, the peak value, and/or the integrated total value.

Systems 30 may comprise a production well 64 that is configured to extract mobile components (e.g., hydrocarbon fluids) from the subterranean formation 28. Extracted mobile components may be hydrocarbons produced in the subterranean formation by in situ pyrolysis. The production well 64 may be fluidically connected, directly or indirectly, to the subterranean formation 28. The production well 64 may be placed in fluidic contact with the subterranean formation 28 generally at any time. For example, the production well 64 may be placed prior to first controlling the in situ resistive heating element 40 and/or prior to the creation of the in situ resistive heating element 40. When present, an electrode well 60 also may serve as a production well 64, in which case the electrode well 60 may be configured to extract mobile components from the subterranean formation 28.

Systems 30 may comprise a controller 34. Controller may control the in situ resistive heater 38, the gas delivery system 36, other components of the system 34, and/or overall operation of the system 30. The controller 34 may record and/or monitor the sensor 32 output. Generally, the controller 34 may be configured to control systems 30 according to any of the methods described herein. For example, the controller may modulate and/or regulate the heating of the in situ resistive heater 38. As another example, the controller may modulate and/or regulate the gas delivery (i.e., the injecting of the one or more control gases 68) by the gas delivery system 36. As another example, the controller may modulate and/or regulate the adjusting of the electrical conductivity of the one or more controlled regions 70 with the one or more control gases 68.

FIG. 2 is a flow chart of examples of methods 10 that may be used to control an in situ resistive heating element 40. Methods 10 may control an in situ resistive heating element by adjusting the electrical conductivity of one or more controlled regions 70 associated with the in situ resistive heating element 40. Methods 10 may comprise heating 11 one or more controlled regions with the in situ resistive heating element. Methods 10 may comprise injecting 12 one or more control gases 68 into one or more controlled regions 70. Methods may comprise adjusting 13 the electrical conductivity of one or more controlled regions with the one or more control gases 68. Performance of methods 10 may result in one or more of growing the in situ resistive heating element 40, limiting the growth of the in situ resistive heating element 40, increasing the spatial extent of the in situ resistive heating element 40, maintaining the active volume of the in situ resistive heating element 40, decreasing the active volume of the in situ resistive heating element 40, concentrating the heating of the in situ resistive heating element 40 near unpyrolyzed subterranean regions, and/or producing hydrocarbons from the subterranean formation 28.

Further, methods 10 may limit the effects of interfering chemical decomposition within the subterranean formation 28. At high enough temperatures, components of the subterranean formation 28 may decompose, generating products that interfere with efficient pyrolysis and/or electrical conductivity enhancement. This decomposition of components that interfere with efficient pyrolysis and/or electrical conductivity enhancement may be referred to as interfering decomposition, and the components that decompose to cause this interfering composition may be referred to as interfering components. For example, carbonate minerals decompose to produce carbon dioxide, an oxidizing gas. By injecting a control gas to counteract the production of interfering components, pyrolysis may continue unabated. Pyrolysis at higher temperatures is generally more effective, at least in that the pyrolysis may occur faster, reducing the time required for heating a subterranean formation 28. For example, methods 10 may provide for efficient continued pyrolysis, and hence continued increase in electrical conductivity and/or production of hydrocarbons, above typical decomposition temperatures of dolomite (about 550° C.) and calcite (about 700° C.).

Methods 10 may comprise iteratively heating 11, injecting 12, and adjusting 13. Heating 11, injecting 12, and adjusting 13 may be performed at least partially concurrently. Heating 11, injecting 12, and adjusting 13 may be performed at least partially sequentially. Heating 11, injecting 12, and adjusting 13 may each independently be performed periodically.

Heating 11 may include electrically powering one or more in situ resistive heating elements 40 to cause resistive heating within the heating element(s) sufficient to heat one or more controlled regions 70. For example, one in situ resistive heating element may be used to heat a plurality of controlled regions. As another example, a plurality of in situ resistive heating elements may be used to heat a single controlled region. In the case of a plurality of controlled regions, heating of each controlled region may be independent, as examples, at least partially concurrent and/or at least partially sequential. In the case of a plurality of in situ resistive heating elements, powering of each heating element may be independent, as examples, at least partially concurrent and/or at least partially sequential. Electrically powering may include transmitting electrical current through an in situ resistive heating element via at least two spaced-apart electrodes 50, which optionally are at least partially contained within one or more electrode wells 60.

Heating 11 may include modulating the heating of one or more controlled regions 70 by changing a characteristic relating to at least one of the duration of heating and the magnitude of heating. For example, heating 11 may be started, stopped, paused, and/or repeated. As other examples, heating 11 may accelerate, decelerate, increase, decrease, and/or include a high power impulse.

Heating 11 may include heating one or more controlled regions 70 to a temperature suitable for pyrolysis. Heating 11 may include electrically powering the in situ resistive heating element 40 for a suitable time to pyrolyze organic matter within the one or more controlled regions 70. For example, heating 11 may include electrically powering for at least one day, at least one week, at least two weeks, at least three weeks, at least one month, at least two months, at least three months, at least four months, at least five months, at least six months, at least one year, at least two years, at least three years, at least four years or and/or within a range that includes or is bounded by any of the preceding examples.

Injecting 12 may include injecting one or more control gases 68 to one or more controlled regions 70. Adjusting 13 may include affecting, or otherwise adjusting, the electrical conductivity of the control region(s) with the one or more control gases 68 upon heating. The one or more control gases may be delivered through one or more injection wells 62. The one or more injection wells 62 may include one or more injection sites 63. One or more control gases may be injected to a plurality of controlled regions. One or more controls gases may be delivered to a single controlled region. One or more control gas may be injected to one controlled region that is different from one or more control gases delivered to another controlled region. Each control gas delivered may be injected through an independent injection well and/or an independent injection site. In the case of a plurality of controlled regions, injection of control gas to each controlled region may be independent, as examples, at least partially concurrent and/or at least partially sequential. In the case of a plurality of control gases, injection of each control gas may be independent, as examples, at least partially concurrent and/or at least partially sequential. Further, a plurality of control gases may be injected to one or more controlled regions through one or more injection wells and/or injection sites. Some injection wells may also serve as electrode wells 60, allowing for injecting 12 to include injecting a control gas at the site of an electrode 50.

Adjusting 13 may include modulating the delivery of control gas 68 to a controlled region 70 by changing a characteristic relating to at least one of a duration of injecting, a control gas composition, a mass of control gas injected, a volume of control gas injected, a flow rate of control gas injected, a temperature of control gas injected, and/or a pressure of control gas injected. For example, injecting 12 and/or adjusting 13 may be started, stopped, paused, and/or repeated. As other examples, the quantity of control gas injected, and other physical parameters, may accelerate, decelerate, increase, decrease, and/or include an impulse.

A control gas 68 may be a gas suitable to affect, or otherwise adjust, the electrical conductivity of a heated subterranean region containing organic matter. Generally, a control gas 68 may affect the chemical environment, and/or the redox state, of a subterranean region when heated.

Injecting 12 may include injecting an oxidizing gas. Adjusting 13 may include decreasing and/or to maintaining the electrical conductivity of a controlled region by oxidizing (e.g., oxidizing residual coke) while pyrolyzing the controlled region. Injecting 12 may include injecting a reducing gas. Adjusting 13 may include increasing and/or to maintaining the electrical conductivity of a controlled region by reducing (and/or inhibiting oxidization) while pyrolyzing the controlled region. Injecting 12 may include injecting a sweep gas. Adjusting 13 may include increasing and/or maintaining the electrical conductivity of a controlled region by limiting the partial pressure (concentration) of oxidizing gases while pyrolyzing the controlled region. Injecting 12 may include selecting a control gas to affect the electrical conductivity of a controlled region and then injecting the selected control gas into the controlled region.

Injecting 12 may include injecting control gas 68 inside, outside, and/or near the in situ resistive heating element 40. When the in situ resistive heating element 40 defines a shell structure with a core volume, injecting 12 may include injecting control gas at least partially within the shell volume and/or the core volume. Injecting 12 may include injecting control gas to limit expansion of an in situ resistive heating element into a restricted region 72.

Methods 10 may comprise regulating 14 the controlled region 70, generally regulating 14 the spatial extent of the in situ resistive heating element 40, and regulating 14 the electrical conductivity of the controlled region. The regulating 14 the spatial extent of the in situ resistive heating element may include one or more of growing the exterior volume, creating an enclosed volume, growing an enclosed volume, maintaining the interior volume, shrinking the interior volume, creating a shell volume, creating a core volume, growing a core volume, growing the exterior volume while maintaining the interior volume, and limiting the expansion of the in situ resistive heating element. For example, growing the exterior volume of an in situ resistive heating element may include increasing the electrical conductivity of a controlled region near and/or intersecting the in situ resistive heating element. As another example, creating an enclosed volume of the in situ resistive heating element may include decreasing the electrical conductivity of a controlled region inside the in situ resistive heating element. As another example, the expansion of an in situ resistive heating element may be limited by decreasing, or at least maintaining below a predetermined threshold, the electrical conductivity of a controlled region adjacent to the in situ resistive heating element. Limiting the expansion of an in situ resistive heating element may include protecting a restricted region 72 from expansion of the in situ resistive heating element.

Regulating 14 the spatial extent of the in situ resistive heating element may include injecting 12 a control gas 68 into a controlled region 70 while expanding the heating element and subsequently injecting a different control gas into the controlled region while continuing to expand the heating element. For example, regulating 14 may include encouraging increased electrical conductivity (by injecting a suitable control gas) in a controlled region within a growing in situ resistive heating element. Then, after a suitable time and/or after the in situ resistive heating element has grown sufficiently, switching the control gas to decrease electrical conductivity in the control region.

Regulating 14 the electrical conductivity of the controlled region 70 may include increasing the electrical conductivity of the controlled region. For example, the electrical conductivity may be increased by one or more of heating to cause pyrolysis, injecting a reducing gas and/or sweep gas, and decreasing the concentration of oxidizing gas. Heating to cause pyrolysis may include increasing the temperature of the corresponding region of the subterranean formation to cause pyrolysis and/or maintaining the temperature of the subterranean formation above a predetermined threshold to cause continued pyrolysis. Decreasing a concentration of oxidizing gas may include producing a reducing gas and/or a sweep gas in situ, and/or ceasing addition of an oxidizing gas. Regulating 14 the electrical conductivity of the controlled region may include decreasing the electrical conductivity of the controlled region, for example by one or more of heating to cause interfering decomposition (e.g., increasing the temperature to cause interfering decomposition, and/or maintaining the temperature above a predetermined threshold to cause continued interfering decomposition), injecting an oxidizing gas, and increasing the concentration of oxidizing gas (e.g., producing an oxidizing gas in situ and/or ceasing addition of sweep gas). Regulating 14 the electrical conductivity of the controlled region may include maintaining the electrical conductivity of the controlled region. Regulating 14 may include maintaining the electrical conductivity above or below a predetermined threshold. Regulating 14 may include maintaining by combinations of heating to increase or decrease electrical conductivity, and adjusting (such as via injecting a control gas) to increase or decrease electrical conductivity. For example, maintaining may include (a) heating to cause pyrolysis and injecting a reducing gas and/or a sweep gas, (b) heating to cause pyrolysis and injecting to decrease the concentration of oxidizing gas, (c) heating to cause pyrolysis and injecting an oxidizing gas, (d) heating to cause pyrolysis and injecting to increase the concentration of oxidizing gas, (e) heating to cause interfering decomposition and injecting a reducing gas and/or a sweep gas, (f) heating to cause interfering decomposition and injecting to decrease the concentration of oxidizing gas, (g) heating to cause interfering decomposition and injecting an oxidizing gas, and/or (h) heating to cause interfering decomposition and injecting to increase the concentration of oxidizing gas.

Regulating 14 may include adjusting heating 11, injecting 12, and/or adjusting 13 based upon a monitored parameter and/or based upon a priori data relating to the subterranean formation 28. A priori data may relate to estimates, models, and/or forecasts of the heating, pyrolyzing, electrical conductivity, injecting, permeability, and/or hydrocarbon production of the subterranean formation 28 and/or a region of the subterranean formation 28. Regulating 14 may include adjusting heating 11, injecting 12, and/or adjusting 13 when a monitored parameter is and/or a priori data are projected to be greater than, equal to, or less than a predetermined threshold. The adjusting may include starting, stopping, and/or continuing heating 11, injecting 12, and/or adjusting 13.

Methods 10 may comprise monitoring 16 the process of adjusting the controlled region 70. The monitoring 16 may form a basis for regulating 14 heating 11, injecting 12, and/or adjusting 13. Monitoring 16 may include monitoring a subterranean parameter relating to at least one of the subterranean formation 28, organic matter in the subterranean formation, the in situ resistive heating element 40, and the controlled region. The subterranean parameter may include at least one of a shape, an extent, a volume, a composition, a density, a porosity, a permeability, an electrical conductivity, an electrical property, a temperature, a pressure, a duration of heating, a magnitude of heating, a gas composition, a chemical environment, a chemical redox state, and hydrocarbon production. The magnitude may include the average value, the peak value, and/or the integrated total value. Monitoring 16 may include monitoring a transmission parameter, a parameter relating to transmitting electrical power through the in situ resistive heating element. The transmission parameter may include at least one of electrical power transmitted, electrical current transmitted, and a duration of the transmitting. Monitoring 16 may include monitoring an injection parameter, namely, a parameter relating to the injecting 12. The injection parameter may include at least one of a duration of injecting, a gas composition, a mass of control gas injected, a volume of control gas injected, a flow rate of the control gas, a temperature of the control gas, and a pressure of the control gas.

Methods 10 may comprise determining 17 a desired growth pattern for the in situ resistive heating element 40. Determining 17 may occur before, during, and/or after one or more of heating 11, injecting 12, and adjusting 13. Determining 17 may be at least partially based on data relating to at least one of the subterranean formation, organic matter in the subterranean formation, the in situ resistive heating element, and one or more controlled regions 70. For example, determining 17 may be based upon geophysical data relating to a shape, an extent, a volume, a composition, a density, a porosity, a permeability, an electrical conductivity, an electrical property, a temperature, a pressure, a gas composition, a chemical environment, and/or a chemical redox state. Determining 17 may include estimating, modeling, forecasting and/or measuring the heating, pyrolyzing, electrical conductivity, injecting, permeability, and/or hydrocarbon production of the subterranean formation 28 and/or a region of the subterranean formation 28. Determining 17 may result in a plan for heating 11, injecting 12, and/or adjusting 13. Determining 17 may result in parameters to control heating 11, injecting 12, and/or adjusting 13. Determining 17 may result in a plan for and/or a layout of electrode wells 60 and/or gas injection wells 62.

Any suitable factors or criteria may be considered when determining 17 where and/or when to place gas injection wells 62 and/or where and/or when to inject control gas 68. For example, the composition of the subterranean formation may be considered. Consideration of the composition of the subterranean formation may include considering intrusions of geophysically distinct/separate regions, natural or manmade fractures, organic matter distribution and/or aquifers. For example, the intruding regions may have much higher or much lower permeability than the bulk of the subterranean formation. High permeability an intruding (or other) region may allow for more efficient fluidic connection across the intruding region. The more efficient fluidic connection may lead to high dissipation of control gas introduced near the intruding region. Low permeability of an intruding (or other) region may lead to barriers to and/or traps for fluid flowing near the intruding region.

Methods 10 may comprise placing 18 gas injection wells 62 into the subterranean formation 28. Placing 18 may include placing at least one gas injection well into fluidic contact with the in situ resistive heating element 40. Placing 18 may include placing at least one gas injection well into fluidic contact with a subterranean region outside of the in situ resistive heating element. Gas injection wells may be placed in anticipation of growth of the in situ resistive heating element. Gas injection wells may be placed to guide and/or direct the in situ resistive heating element towards subterranean regions of potentially higher productivity and/or of higher organic matter content. Gas injection wells may be placed to guide and/or direct the in situ resistive heating element away from restricted region(s) 72.

Generally, placing 18 gas injection wells 62 may occur at any time. Placing 18 a gas injection well 62 may be more convenient and/or practical before heating the portion of the subterranean formation 28 that will neighbor (i.e., be adjacent to), much less include, the placed gas injection well. For example, drilling a well may be difficult at temperatures above the boiling point of drilling fluid components. Placing 18 may occur after determining 17 a desired growth pattern for the in situ resistive heating element.

Methods 10 may comprise placing 19 electrode wells 60 into the subterranean formation 28 and/or placing 19 electrodes 50 into electrical contact with at least a portion of the subterranean formation. For example, placing 19 may include placing two or more electrodes into electrical contact with the in situ resistive heating element 40. Placing 19 may include placing at least one electrode outside of the in situ resistive heating element. Electrodes and/or electrode wells may be placed in anticipation of growth of the in situ resistive heating element. Electrodes may be placed to guide and/or direct the in situ resistive heating element toward subterranean regions of potentially higher productivity and/or of higher organic matter content. Electrodes may be placed to guide and/or direct the in situ resistive heating element away from restricted regions.

Placing 19 electrode wells 60 and/or electrodes 50 may occur at any time. Placing 19 an electrode may be more convenient and/or practical before heating the portion of the subterranean formation 28 that will neighbor (i.e., be adjacent to), much less include, the placed electrode and/or electrode well. For example, drilling a well may be difficult at temperatures above the boiling point of drilling fluid components. Placing 19 may occur after determining 17 a desired growth pattern for the in situ resistive heating element.

Further, performance of methods 10 may change the shape of an in situ resistive heating element 40 into a more useful form. Several examples of types of changes are represented schematically in FIGS. 3-7. As represented in FIG. 3, methods 10 may include creating a shell-form in situ resistive heating element by decreasing the average electrical conductivity of a portion of the interior volume (the controlled region 70) sufficient to create (and/or grow) a relatively electrically non-conductive core volume (an enclosed volume 83). Decreasing the average electrical conductivity may be performed as above, e.g., by injecting an oxidizing control gas 68 through a gas injection well 62, and/or ceasing the injection of a sweep gas. The creation of a shell-form heating element may include shrinking the interior volume 82 of the heating element. A shell-form heating element may concentrate the active heating in the shell to the subterranean region near the outside of the heating shell, which typically will contain unpyrolyzed rock. Concentrating the active heating to this exterior region may avoid unnecessary heating of the potentially heavily pyrolyzed core volume. A shell-form heating element may have reduced electrical power requirements (because of the reduced active volume) relative to a same-sized (exterior volume) heating element without any enclosed volume.

As represented in FIG. 4, methods 10 may include splitting an in situ resistive heating element 40 into two or more in situ resistive heating elements 40. Splitting may include decreasing the average electrical conductivity of a portion of the interior volume (the controlled region 70) sufficient to split the original in situ resistive heating element into two or more independent, electrically-disconnected, in situ resistive heating elements. Decreasing the average electrical conductivity may be performed as above, e.g., by injecting an oxidizing control gas 68 through one or more gas injection wells 62, and/or ceasing the injection of a sweep gas. If the controlled region is heavily pyrolyzed, the electrically powering the split heating elements, rather than the source (whole) heating element, may more effectively concentrate heating on less pyrolyzed subterranean regions, away from one or more controlled regions. Splitting an in situ resistive heating element into two or more in situ resistive heating elements also may result in reduced electrical power requirements (because of the reduced active volume) relative to the source heating element. Moreover, the split in situ resistive heating elements may be independently controlled, leading to more flexibility in pyrolyzing the subterranean formation with the heating elements.

As represented in FIG. 5, methods 10 may include at least partially shrinking an enclosed volume 83 (the controlled region 70) within an in situ resistive heating element 40 (and/or grow the interior volume 82). At least partially shrinking the enclosed volume may occur by increasing the average electrical conductivity of the enclosed volume sufficient to allow transmitted electrical current to resistively heat at least a portion of the enclosed volume. Increasing the average electrical conductivity may be performed as above, e.g., by ceasing the injection of an oxidizing control gas 68 through a gas injection well 62 and/or continued heating 11 of the controlled region.

Methods 10 may include decreasing the average electrical conductivity of a controlled region 70 adjacent to, and intersecting with, an in situ resistive heating element 40 to shrinking the exterior volume 81 at least in one direction (FIG. 6). Decreasing the average electrical conductivity may be performed as above, e.g., by injecting an oxidizing control gas 68 through a gas injection well 62, and/or ceasing the injection of a sweep gas. The gas injection well may have an extended gas injection site 63 that is substantially parallel to an elongated direction of the in situ resistive heating element and/or at least one electrode 50.

Methods 10 may include limiting expansion of an in situ resistive heating element 40 into a restricted region 72 by decreasing the average electrical conductivity of a controlled region 70 between the in situ resistive heating element and the restricted region (FIG. 7). Decreasing the average electrical conductivity may be performed as above, e.g., by injecting an oxidizing control gas 68 through a gas injection well 62, and/or ceasing the injection of a sweep gas. The gas injection well may have an extended gas injection site 63 that is substantially parallel to an elongated direction of the in situ resistive heating element, the restricted region, and/or at least one electrode 50.

Several of the illustrative, non-exclusive examples have been discussed and/or presented in the context of flow diagrams, or flow charts, in which the methods are shown and described as a series of blocks, or steps. Unless specifically set forth in the accompanying description, the order of the blocks may vary from the illustrated order in the flow diagram, including with two or more of the blocks (or steps) occurring in a different order and/or concurrently.

As used herein, the term “and/or” placed between a first entity and a second entity means one of (1) the first entity, (2) the second entity, and (3) the first entity and the second entity. Multiple entities listed with “and/or” should be construed in the same manner, i.e., “one or more” of the entities so conjoined. Other entities may optionally be present other than the entities specifically identified by the “and/or” clause, whether related or unrelated to those entities specifically identified.

As used herein, the phrase “at least one,” in reference to a list of one or more entities should be understood to mean at least one entity selected from any one or more of the entity in the list of entities, but not necessarily including at least one of each and every entity specifically listed within the list of entities and not excluding any combinations of entities in the list of entities. This definition also allows that entities may optionally be present other than the entities specifically identified within the list of entities to which the phrase “at least one” refers, whether related or unrelated to those entities specifically identified.

In the event that any patents, patent applications, or other references are incorporated by reference herein and (1) define a term in a manner that is inconsistent with and/or (2) are otherwise inconsistent with, either the non-incorporated portion of the present disclosure or any of the other incorporated references, the non-incorporated portion of the present disclosure shall control, and the term or incorporated disclosure therein shall only control with respect to the reference in which the term is defined and/or the incorporated disclosure was present originally.

As used herein the terms “adapted” and “configured” mean that the element, component, or other subject matter is designed and/or intended to perform a given function. Thus, the use of the terms “adapted” and “configured” should not be construed to mean that a given element, component, or other subject matter is simply “capable of” performing a given function but that the element, component, and/or other subject matter is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the function. It is also within the scope of the present disclosure that elements, components, and/or other recited subject matter that is recited as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa.

As utilized herein, the terms “approximately,” “about,” “substantially,” and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numeral ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and are considered to be within the scope of the disclosure.

INDUSTRIAL APPLICABILITY

The systems and methods disclosed herein are applicable to the oil and gas industry.

The subject matter of the disclosure includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. Similarly, where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.

It is believed that the following claims particularly point out certain combinations and subcombinations that are novel and non-obvious. Other combinations and subcombinations of features, functions, elements and/or properties may be claimed through amendment of the present claims or presentation of new claims in this or a related application. Such amended or new claims, whether different, broader, narrower, or equal in scope to the original claims, are also regarded as included within the subject matter of the present disclosure. 

1. A method of controlling an in situ resistive heating element within a subterranean formation containing a controlled region, the method comprising: heating the controlled region with the in situ resistive heating element; injecting a control gas into the controlled region; and adjusting the electrical conductivity of the controlled region with the control gas.
 2. The method of claim 1, wherein the control gas is an oxidizing gas, and wherein the adjusting includes decreasing the electrical conductivity of the controlled region with the control gas.
 3. The method of claim 1, wherein the control gas is a reducing gas, and wherein the adjusting includes inhibiting oxidization of the controlled region.
 4. The method of claim 1, wherein the control gas is a sweep gas, wherein the adjusting includes reducing the partial pressure of oxidizing gas within the controlled region.
 5. The method of claim 1, wherein the heating includes modulating the heating by changing a heating parameter, wherein the heating parameter relates to at least one of a duration of heating and a magnitude of heating.
 6. The method of claim 1, wherein the adjusting includes modulating the injecting by changing an injection parameter, wherein the injection parameter relates to at least one of a duration of injecting, a control gas composition, a mass of control gas injected, a volume of control gas injected, a flow rate of control gas injected, a temperature of control gas injected, and a pressure of control gas injected.
 7. The method of claim 1, further comprising regulating the electrical conductivity of the controlled region by the heating, the injecting, and the adjusting.
 8. The method of claim 1, wherein the regulating includes increasing the electrical conductivity of the controlled region.
 9. The method of claim 1, wherein the regulating includes decreasing the electrical conductivity of the controlled region.
 10. The method of claim 1, wherein the regulating includes maintaining the electrical conductivity of the controlled region.
 11. The method of claim 1, further comprising regulating a spatial extent of the in situ resistive heating element by the heating and the injecting.
 12. The method of claim 11, wherein the regulating includes growing an exterior volume of the in situ resistive heating element.
 13. The method of claim 11, wherein the regulating includes growing an exterior volume of the in situ resistive heating element while maintaining an interior volume of the in situ resistive heating element.
 14. The method of claim 11, wherein the controlled region is adjacent to a restricted region of the subterranean formation; and wherein the regulating includes limiting expansion of the in situ resistive heating element into the restricted region by decreasing the electrical conductivity of the controlled region.
 15. The method of claim 11, wherein the controlled region is adjacent to a restricted region of the subterranean formation; and wherein the regulating includes limiting expansion of the in situ resistive heating element into the restricted region by maintaining the electrical conductivity of the controlled region below a predetermined threshold.
 16. The method of claim 11, wherein the heating expands the spatial extent of the in situ resistive heating element, wherein the injecting includes injecting a first control gas into the controlled region while expanding the in situ resistive heating element, and wherein the injecting includes subsequently injecting a second control gas into the controlled region while expanding the in situ resistive heating element.
 17. The method of claim 1, wherein the injecting includes injecting a plurality of control gases into the controlled region.
 18. The method of claim 1, wherein the heating includes heating a plurality of controlled regions with the in situ resistive heating element, and wherein the injecting includes injecting into the plurality of controlled regions by injecting one or more control gases into each of the plurality of controlled regions.
 19. The method of claim 18, wherein the injecting includes injecting a first control gas into one of the controlled regions and injecting a second control gas into another of the controlled regions, wherein the second control gas is different from the first control gas.
 20. The method of claim 1, wherein the controlled region is within an interior volume of the in situ resistive heating element, and wherein the adjusting decreases the average electrical conductivity of a portion of the interior volume sufficient to split the in situ resistive heating element into two or more independent, electrically-disconnected, in situ resistive heating elements.
 21. The method of claim 1, further comprising monitoring a subterranean parameter relating to at least one of the subterranean formation, organic matter in the subterranean formation, the in situ resistive heating element, and the controlled region, wherein the subterranean parameter includes at least one of a shape, an extent, a volume, a composition, a density, a porosity, a permeability, an electrical conductivity, an electrical property, a temperature, a pressure, a duration of heating, a magnitude of heating, a gas composition, a chemical environment, a chemical redox state, and hydrocarbon production; and further wherein the adjusting includes regulating injection of control gas based at least in part on the subterranean parameter.
 22. The method of claim 1, further comprising monitoring a subterranean parameter relating to at least one of the subterranean formation, organic matter in the subterranean formation, the in situ resistive heating element, and the controlled region, wherein the subterranean parameter includes at least one of a shape, an extent, a volume, a composition, a density, a porosity, a permeability, an electrical conductivity, an electrical property, a temperature, a pressure, a duration of heating, a magnitude of heating, a gas composition, a chemical environment, a chemical redox state, and hydrocarbon production; and further wherein the heating includes regulating heating based at least in part on the subterranean parameter.
 23. The method of claim 1, wherein the heating includes transmitting electrical power through the in situ resistive heating element, and the method further comprising monitoring a transmission parameter, wherein the transmission parameter includes at least one of electrical power transmitted, electrical current transmitted, and a duration of the transmitting; and further wherein the adjusting includes regulating injection of control gas based at least in part on the transmission parameter.
 24. The method of claim 1, wherein the heating includes transmitting electrical power through the in situ resistive heating element, and the method further comprising monitoring a transmission parameter, wherein the transmission parameter includes at least one of electrical power transmitted, electrical current transmitted, and a duration of the transmitting; and further wherein the heating includes regulating heating based at least in part on the transmission parameter.
 25. The method of claim 1, further comprising monitoring an injection parameter, wherein the injection parameter includes at least one of a duration of injecting, a gas composition, a mass of control gas injected, a volume of control gas injected, a flow rate of the control gas, a temperature of the control gas, and a pressure of the control gas; and further wherein the adjusting includes regulating injection of control gas based at least in part on the injection parameter.
 26. The method of claim 1, further comprising monitoring an injection parameter, wherein the injection parameter includes at least one of a duration of injecting, a gas composition, a mass of control gas injected, a volume of control gas injected, a flow rate of the control gas, a temperature of the control gas, and a pressure of the control gas; and further wherein the heating includes regulating heating based at least in part on the injection parameter.
 27. The method of claim 1, further comprising selecting the control gas to adjust the electrical conductivity of the controlled region.
 28. A system for controlling an in situ resistive heating element within a subterranean formation containing a controlled region, the system comprising: an in situ resistive heater configured to heat the controlled region, the in situ resistive heater including: an in situ resistive heating element within the subterranean formation electrically connected to two or more spaced-apart electrodes; and an electrical power source electrically connected through a pair of spaced-apart electrodes to the in situ resistive heating element; a gas delivery system configured to inject a control gas into the controlled region and to adjust an electrical conductivity of the controlled region with the control gas, the gas delivery system including: a gas injection well fluidically connected to the controlled region; and a gas source configured to supply the control gas to the gas injection well, wherein the control gas is selected to adjust the electrical conductivity of the controlled region; and a sensor to monitor a parameter relating to at least one of the subterranean formation, the in situ resistive heater, the gas delivery system, and the controlled region, wherein the parameter includes at least one of an electrical conductivity, an electrical property, an electrical power, an electrical current, a temperature, a pressure, a gas composition, a chemical environment, and a chemical redox state.
 29. The system of claim 28, wherein the gas delivery system is configured to selectively inject one or more control gases based at least in part on the parameter.
 30. The system of claim 28, wherein the gas delivery system includes a plurality of control gases, wherein at least one of the control gases is selected to increase and/or maintain an electrical conductivity within a portion of the subterranean formation when the portion is heated, and wherein at least one of the control gases is selected to decrease an electrical conductivity within a portion of the subterranean formation when the portion is heated.
 31. The system of claim 28, wherein the subterranean formation includes a plurality of controlled regions, wherein the gas delivery system includes a plurality of gas injection wells, each gas injection well fluidically connected to at least one controlled region. 